Radio communications involves either one-way (e.g. selective call signalling or paging systems) or two-way communications (cellular, cordless telephone, or digital personal communication systems) over radio waves. Communication takes place on channels, comprising time division multiplexed (TDM) timeslots or frequency division multiplexed (FDM) frequencies, or a combination thereof.
For various radio communications, fixed radio frequency spectrum are assigned. For example, in the United States, the Federal Communications Commission reserves various portions of the radio frequency spectrum to designated communication services. The radio frequency use is therefore limited to assigned services. The radio frequency use is more overtaxed within certain areas where the number of frequencies allocatable for communicating between radio transceivers in a system are severely limited.
As communication between radio transceivers is initiated, the system allocates a channel or channels for communication service therebetween. With the increase in radio communications, such as cellular and cordless telephone usage, the method for allocating channels must allocate channels utilizing the assigned frequencies in a manner to accommodate ever increasing concurrent users. Signal interference may result from multiple simultaneous usage of the same channel in neighboring geographical areas (co-channel interference) or usage of adjacent channels in the same geographical areas. The resulting interference reduces the level of system service quality. It is therefore a primary concern of the system operator to allocate channels for communication in a manner to allow the greatest efficiency of usage while reducing interference in order to maintain a certain level of service quality.
There are generally two types of channel allocation methods: fixed channel allocation and dynamic channel allocation. Fixed channel allocation methods fix the channel assignments during the entire course of operation. Since the channels are allocated only once, the fixed channel allocation method can be very time intensive and, therefore, have a good chance to provide a high level of channel reuse for any given conditions. Fixed channel allocation methods are simple and may approach being optimal in terms of channel reuse to any given traffic pattern for a given system. But the fixed channel allocation is not adaptive to a changing service environment. Also, to add or remove a base station from the system is cumbersome and fixed channel allocation methods are unable to automatically initialize the channel allocation.
Dynamic channel allocation methods, on the other hand, allocate channels in accordance with a method which is adaptive to traffic and environment changes. Since dynamic channel allocation methods do not assign channels, channels can be used in any area as needed. In addition, most dynamic channel allocation methods can initialize automatically. Unfortunately most of the existing dynamic channel allocation methods are too dynamic to have good performance in terms of channel reuse.
Generally, dynamic channel allocation methods have better performance than fixed channel allocation methods in light and unevenly distributed traffic. However in heavy traffic, typical dynamic channel allocation methods perform worse than fixed channel allocation methods.
Thus, what is needed is a method and apparatus for channel allocation which combines the benefits of fixed channel allocation methods and dynamic channel allocation methods that is adaptive to the slowly changing environment while approaching the maximum system capacity with acceptable service quality for any environment.